It’s Superbird!

In 1952, a proof Washington Quarter was produced containing a letter "S" on the eagle's chest on the reverse side of the coin. After its discovery, collectors quickly referred to it as the Superbird Quarter, comparing it to the Superman hero character. In the 1950s, the Superman TV show was so extremely popular that some experts believe that a Mint employee intentionally added the "S' mint mark on the eagle's chest as a way of supporting the Superman show. It's now been over 50 years since its discovery and no further information has developed on how this variety occurred, and more than likely we will just never know. But one thing is for certain - this is a very interesting variety.

The lower die, usually the reverse – although on some issues with striking problems, the obverse was employed as the lower die. Because of the physics of minting, the fixed lower-die impression is slightly better struck than the upper-die impression.